1. Technical Field
The invention relates to an apparatus in the form of an arrangement of rollers, in particular embossing rollers, and at least one conveyor belt in the form of a transfer belt, for fleece production and in particular for airlaid production. By the term airlaid production is meant the manufacturing of nonwoven, fleece-like fiber products with fiber lengths of up 50 millimeters.
2. Discussion of Related Art
In many cases, such products are intermediate products required for a wide range of final products such as sanitary towels, wiping cloths or absorbent material for the automotive industry. Nonwoven fabrics are produced from natural or synthetic fibers made of different material and with different staple lengths. A bonding agent such as Latex can be used to bond the fibers together. In the case of plastic fibers, bonding can also be effected by partially melting and fusing the fibers with each other. The nonwoven fabric to be produced—including the intermediate product—may have a multilayered structure. To provide the nonwoven fabric with a particularly high fluid uptake capacity, superabsorbent polymers in particle (SAP) or fiber form (SAF) can be added.
Suitable natural fibers include, for example, cellulose fibers from cotton, hemp or flax, or loosened wood cellulose that has already been mechanically or chemically treated (fluff pulp). Suitable plastic fibers, particularly matrix fibers used for bonding the nonwoven fabric, can contain polyester, polypropylene or viscose. Particularly suitable synthetic bonding fibers are bicomponent fibers, so called, which have a core made of a first material surrounded by a mantle made of a plastic, for example polyethylene, which allows the fibers to fused with each other and with natural and matrix fibers.
The range of desired densities of the product is heavily dependent on the final product for which the nonwoven fabric is to be used. The range of desired fleece densities is very large, therefore. The range of materials to be processed (see above) and the range of staple lengths of the single fibers is likewise very large.
The production of an airlaid nonwoven fabric of the kind involved here usually includes mixing the fibers in a forming head which is disposed above a forming belt in the form of an air-permeable conveyor belt, and which spreads the processed mixed fibers as uniformly as possible on the forming belt. Suction boxes, with which the fibers deposited on the forming belt are sucked onto the forming belt, are disposed underneath the forming belt. Downstream from the forming head, in the direction of the forming belt (also called a forming sieve), a compacting roller is generally provided which acts from above on the fiber-air mixture deposited on the forming belt and which pre-compresses said mixture. Air is pressed out of the fiber-air mixture in the process, with the result that the mixture decreases in thickness and increases in density. The fiber-air mixture pre-compacted in this manner is then transferred from a forming belt to a transfer belt which is located above the pre-compacted fiber-air mixture and is permeable to air, such that the fiber-air mixture is sucked onto the transfer belt from below by means of a suction box disposed above the transfer belt, and received by the forming belt. The transfer belt is used to feed the pre-compacted fiber-air mixture to the roller arrangement of interest here for further compaction of the fiber-air mixture into a fleece.
The roller arrangement of interest here is used to compact the fiber-air mixture and, in one preferred embodiment, to bring about the fusing of single fibers by heating the fiber-air mixture—possibly with simultaneous embossing of a structure—such that a nonwoven fabric is produced as an intermediate product with the desired properties.
This kind of apparatus described here is intended to be suitable for producing a wide range of products that, as described at the beginning, may differ considerably in their composition, and which accordingly require different kinds of treatment. For example, the amount of heat required to melt the fibers differs considerably depending on the composition of the fiber-air mixture and the desired thickness and density of the starting material. At the same time, steps should be taken to ensure, if possible, that the fiber-air mixture fed by the transfer belt is always in step and is further processed in a uniform manner and, in particular, is further compacted. During compaction, it is important to prevent wave-like variations in density occurring in the direction that the nonwoven fabric is conveyed, which may arise, for example, when the fiber material to be compacted periodically dams up in front of a roller pair that effects such compaction. One problem in this context consists, for example, in the fact that the air to be pressed out of the fiber-air mixture during compaction must escape in the direction opposite to the conveying direction. In the worst case, an air cushion is produced that can even lead to unwanted folds forming in the nonwoven fabric.
There is therefore a need for an apparatus that is suitable for producing a large range of products.